(Beyond Pesticides, August 12, 2021) A recent study published in Chemosphere identifies the concentration, consequences, and potential sources of 22 organochlorine pesticides (OCPs) among corals in the South China Sea (SCS) for the first time. SCS corals exhibit a higher affinity toward bioaccumulation of OCPs, which are legacy persistent organic pollutants (POPs) under the Stockholm Convention—a global treaty to eliminate POPs. The study finds the distribution of OCPs in coral tissue matches that of the surrounding oceanic air samples. Hence, atmospheric concentrations of OCPs—influenced by continental air masses—migrate from the atmosphere to seawater through gas exchange.
Coral reefs are one of the largest ecosystems in the ocean, sustaining marine biodiversity and providing many goods and services. However, living coral populations are rapidly declining due to ocean acidification, oceanic warming, habitat destruction, and pollution from human activity across the globe. From rare corals off the coast of Florida to well-established hard corals in the Great Barrier Reef, these communal organisms are sensitive to various environmental stressors that threaten biodiversity. Although several studies demonstrate the volatile, toxic nature of POPs, much less research evaluates the impact POPs have on biodiversity over time. The globe is currently going through the Holocene Extinction, Earth’s 6th mass extinction, with one million species of plants and animals at risk. With the increasing rate of biodiversity loss, advocates say it is essential for government agencies to research how previous and ongoing use of POPs can impact present-day species. Likewise, collaborative, global monitoring of POPs can help leaders identify the effect on vulnerable species of the chemicals’ long-range transport and the most effective unified global strategy. The researchers note, “Understanding the dynamics of air-seawater exchange and the within-ocean processing of POPs in the SCS is critical to obtain better insight into their global fate and behavior.”
Researchers investigated the occurrence, taxonomic profiles, and geographical distribution of organochlorine pesticides in coral tissue. They compared results to ambient air and seawater OCP distribution/concentration from the South China Sea. Target chemicals included 22 OCPs: six DDT compounds, four hexachlorocyclohexane compounds (HCHs), five chlordane compounds (CHLs), heptachlor, heptachlor epoxide A and B, two endosulfans (ENDOs), hexachlorobenzene (HCB), p,p′-methoxychlor (MXC), and three Drins (aldrin, endrin, and dieldrin). Using gas chromatography-tandem, researchers measured OCP concentration in SCS coral tissue, air, and water samples.
The study results indicate 17 of the 22 OCPs are detectable in seawater, and all 22 OCPs are detectable in ambient air samples from the SCS. The most prominent chemicals amid air and water samples are CHLs, HCBs, DDTs, and Drins. Although coastal corals have higher chemical concentrations than offshore species, the chemical composition is similar, with DDT and CHL compounds dominant among tissue samples. Researchers attribute the difference in OCP concentration among coastal and offshore corals to oceanic currents and storms influencing pollution distribution.
Long-range atmospheric transport and condensation are significant contributors to the global contamination of environmental pollutants like OCPs. Most concerning are the persistent properties of OCPs that allow these substances to remain in the environment long after use. Some of these long-lived chemicals include regionally banned pesticides that are highly toxic to humans and animals: DDT, heptachlor, and lindane. These pesticides cause various adverse effects, from respiratory issues, nervous system disorders, and birth deformities to various common and uncommon cancers. Although some, but not all, manufacturing and use of specific OCPs have declined in the U.S., OCPs remain a global issue, as much of the developing world still report usage. Continued manufacturing and utilization of OCPs increase the probability of long-range transport of these chemicals and their deposition across the globe via precipitation. However, OCPs still mobilize and accumulate in regions void of industrial or agricultural activities, like glacier tops and remote territories. Arctic snowmelt threatens to re-release chemicals entrapped in ice, further contributing to toxic chemical transportation and passive pesticide exposure globally. The glacial melting caused by the climate crisis will only add to atmospheric and waterway contamination. The release of volatile OCPs will enter waterways at the same concentration levels as before ice entrapment, even after several decades.
Pesticide contamination is already a global issue. Clean air, water, and healthy soils are integral to ecosystem function to support life. However, toxic pesticide residues readily contaminate all ecosystems, frequently existing in soils, water (solid and liquid), and the surrounding air at levels exceeding U.S. Environmental Protection Agency (EPA) set standards. Scientific literature demonstrates pesticides’ long history of adverse effects on the environment, including wildlife, biodiversity, and human health. Pesticides can present acute and long-term health impacts worldwide, especially to farmers, 44 percent of whom experience pesticide poisoning every year. Furthermore, a recent study discovered DDT metabolite (DDE’) residues are detectable in residents of Chicago who consume more glasses of tap water per day. Therefore, the ubiquitous nature of pesticides impacting all ecosystems and the health of their inhabitants is a cause of concern for future human, animal, and environmental well-being.
Although this study is the first to identify organochlorine pesticides in corals specific to the South China Sea, numerous studies identify risks to coral reef habitats from chemical pollution. In March 2020, coverage of a report by the Australian government showed that agricultural pesticides are severely damaging the Great Barrier Reef. A University of Queensland study finds pesticide mixtures discharging from rivers and streams contaminate the Great Barrier Reef Lagoon, with 99.8 percent of samples containing up to 20 different pesticide compounds. Moreover, the combined impact, or synergism, between pesticides and warmer oceanic temperatures puts coral reef fish at a greater risk of adverse health effects, including endocrine disruption. The discovery of such intensive penetration of pesticides among coral reefs adds to the growing record of damage on these marine ecosystems.
Overall, OCP concentrations are declining in the South China Sea as many nations ban organochlorine compounds, yet chemical concentrations remain highest in corals near continental areas. The study identifies various routes of OCP exposure among corals, including dietary uptake and partitioning behavior or absorption. Isomer ratios reveal that most OCP contamination stems from the current use of technical chlordane (termiticide) and historical uses of other OCPs. Previous records indicate air and sediments from China, Vietnam, and Pakistan contain inputs of chlordane and DDTs. However, researchers find higher levels of DDT among the coral population relative to chlordane, due to the extensive use of the chemical in counties around the South China Sea. India and Vietnam permit the use of DDT to control mosquitoes under the Stockholm Convention. Furthermore, high temperatures and chemical volatility play a role in organochlorine pesticide availability as primarily gas residues rather than particles in the SCS. Thus, researchers determine that atmospheric deposition of OCPs is a main route of contamination among corals in the SCS. The study concludes, “The present study provides baseline data for future studies of OCPs in CRRs. Nevertheless, studies linking pollution monitoring and ecotoxicology are needed to assess the potential environmental effect of OCPs on corals in future studies. Additionally, analyzing the level of OCPs on a larger temporal-spatial scale is needed.”
Chemical contamination is ubiquitous in marine environments. Consequently, it is essential to understand the impacts of interactions with other environmental pollutants, especially in contaminated ecosystems like waterways. Furthermore, climate crisis implications like melting glaciers present a new concern over the high levels of chemical concentrations in the oceans from DDT, its metabolites, and other persistent organic pollutants, trapped in ice. Therefore, to protect the nation’s and world’s waterways and reduce the number of pesticides that make their way into drinking water, toxic pesticide use must end.
Beyond Pesticides has long advocated for federal regulation that considers potential synergistic and additive threats to ecosystems and organisms. Replacing pesticides with organic, nontoxic alternatives is crucial for safeguarding public health, particularly communities vulnerable to pesticide toxicity. Learn more about pesticide hazards and their impact on wildlife through Beyond Pesticides’ wildlife program page. For more information about pesticide contamination in water, see the Threatened Waters program page and Beyond Pesticides’ article Pesticides in My Drinking Water? Individual Precautionary Measures and Community Action.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.